1. Field of the Invention
This invention relates to a golfclub, and more particularly to a "wood" type golfclub head structure made of stainless steel.
2. Prior Art
Ever since the beginning of golf history, there have been recognized two types of golfclubs; one is called "iron" clubs which have a relatively short shaft with a small "iron" head designed to hit a golf ball accurately and the other is called "wood" clubs which have a relatively long shaft with a large "wood" head designed to hit a ball for a longer distance.
The head portion of the "wood" clubs is traditionally made of solid wood block. Until recently, persimmon was considered to be the most desirable material because of its high impact resistance and fine sound effect. In addition, golfers favored the well-balanced configuration of the traditional persimmon club heads. Particularly, the smooth tapered line in its neck portion has been highly appreciated. With these and other reasons, persimmon wood clubs substantially predominated the market for a long time.
However, as the demand for good persimmon material grew, the natural source of persimmon became scarce. As a result manufactorers find it rather difficult to satisfy all the market. In an attempt to meet the growing market demand, a number of suggestions and proposals have been made in terms of substitute for natural persimmon.
By way of example, U.S. Pat. No. 3,591,183 discloses a laminated golfclub head which is constructed of wood lamination bonded together and bent to form the angle between striding portion and hosel. U.S. Pat. No. 4,204,684 teaches the use of acrylonitrilebutadiene-styrene (ABS) and other plastic materials. U.S. Pat. No. 4,326,716 discloses a clubhead made of vulcanized polyurethane. In addition, steel made "wood" clubs have been disclosed by U.S. Pat. Nos. 3,761,095, 4,021,047, 4,139,196, 4,214,754, 4,319,752 and many others.
Among these substitute materials, stainless steel has recently acquired a significant part of the marketplace.
In general, a stainless steel "wood" club has a clubhead made of stainless steel having a basic shape similar to the conventional persimmon wood club. Its head portion includes an enclosed hollow body defining a hitting surface, a top wall, a sole member, side walls and a neck.
It has been recognized that stainless steel has certain advantages over natural persimmon, such as lower material cost, durability, and less complex finishing process. However, it has been noticed that stainless steel suffers from some disadvantages.
The most critical problem of stainless steel as a substitute for persimmon exists in its weight balance.
Stainless steel is relatively heavy in nature. Thus, it is necessary to have the walls very thin in order to maintain the same total weight as a persimmon head. On the other hand, it is required to have certain thickness to secure sufficient impact resistance and durability. In particular, since the neck portion has been considered to be weak (see U.S. Pat. No. 4,326,716, col. 2, lines 44 and 45), there is a limit to reduce the thickness of the neck portion. As a consequence, the side adjacent to the neck portion (called "heel") tends to have more weight than the other side ("toe"). This causes the center of gravity (sweet-spot) to shift toward the heel side resulting in more deflection in hitting a ball.
The existing solutions to this problem are to have the whole head portion substantially smaller than the traditional persimmon club and/or to have a straight cylindrical neck portion with its lower portions flared to be connected to the head portion as shown FIG. 1. The above solutions have cured the problem to an extent; nonetheless, those solutions have failed to construct a "wood" club head having the size and the configuration which golfers have been enjoying with the traditional persimmon heads.
Therefore, the existing stainless steel "wood" clubs have not superseded qualified persimmon wood clubs.